1. Field of the Invention
The present invention relates generally to x-ray systems and devices. More particularly, embodiments of the invention concern a cathode head that includes features directed to facilitating implementation of focal spot control.
2. Related Technology
It is often desirable in various types of x-ray tubes to be able to deflect the beam of electrons emitted by the cathode, or other emitter, so that the focal spot created by the electron beam can be located at a particular place on the target surface of the anode at which the electron beam is directed. In some instances, the position of the focal spot on the target surface of the anode must be adjusted in order compensate for any changes to the focal spot location that may have resulted from environmental factors, or factors relating to the operation of the x-ray tube.
By way of example, the high speed motion associated with the operation of rotating anode x-ray tubes may cause undesirable variations to a location of the focal spot on the target surface. Further, misalignment of the focal spot on the target surface of the anode can occur over a period of time as the parts of the x-ray device experience operational wear and tear. A variety of other conditions or advance may likewise cause undesirable changes to the desired position of the focal sport on the target surface of the anode.
In yet other cases, it is desirable to move the position of the focal spot on the target surface of the anode so as to achieve a particular x-ray emissive effect or to overcome certain conditions that may be present. Accordingly, the ability to achieve and/or maintain such a desired effect is materially compromised by uncontrolled changes to the position of the focal spot. As an example, it may be desirable in some instances to modify the position of the focal spot in order to compensate for any localized deterioration or other shortcomings in the target surface of the anode. Finally, modification of the position of the focal spot on the target surface of the anode may be necessary in some instances to compensate for local electrical and/or magnetic effects.
Various systems and components have been devised in an effort to attain and maintain effective and reliable focal spot placement and control. For example, deflection of the emitted electron beam and, thus, changes to the position of the focal spot on the target surface of the anode may be implemented through the use of magnetic coils, or electromagnets located on the outside of the x-ray tube.
One significant problem with this type of implementation is that a relatively high level power is required to create the magnetic field necessary to move the focal spot to a desired location or position. Such high power levels relate to the fact that magnetic field strength diminishes over distance. In particular, magnetic coils located on the outside of the x-ray tube, or at other locations well away from the electron beam, require relatively more power to implement a particular electron beam effect than would a magnetic coil, or coils, located relatively closer to the electron beam.
Moreover, known x-ray tube configurations, and cathode assemblies and devices in particular, largely preclude arrangement of a magnetic coil near the electron beam. Further, it is not feasible to locate magnetic coils near the anode due to the high operating temperature of the anode and the presence of x-rays and backscatter electrons that could impair the operation of the coil.
Accordingly, what is needed is a cathode head that includes one or more magnetic elements that are located proximate the emitter so as to enable reliable control of electron beam focal spot location without requiring a significant amount of operational power.